Electronic musical instrument



Patented June 4, 1946 UNITED STATES PATENT OFFICE 2,401,372 ELECTRONIC MUSICAL INSTRUMENT Application December 31, 1942, Serial No. 470,893

- Claims.

1 This invention relates to an improvement in instruments for the production of music with particular reference to the use of electronic devices for generating musical tones. Thein'vention provides an apparatus and a method for adding to tones so generated the effect of auditorium reverberation. I i

It has long been recognized that the sonorousness of the organ, for example, is in great measure due to the reverberation or repeated reflections of the subsiding organ 'tone in a properly designed auditorium. Not only does the reverberation prolong the decaying of the sound, but standing wave patterns are produced in the reverberant space. which shift in location as the sound decays and so result for any individual listener in a fluctuation in the rate of subsidence of the sound. In addition, the air of the auditorium has its own proper frequencies of vibration determined by the auditorium size and shape and these proper frequencies make themselves apparcut as a pitch fluctuation in the decaying tone.

Means are well known for generating musical tones by electronic devices. Likewise means are known to the prior art for controlling. the rate of decay of such tones but it has hitherto been impossible to superimpose on this control of decay a complete simulation of the effect of a satisfactory auditorium. To do so requires, as just stated, the addition to the decaying sound of fluctuations in pitch and in amplitude, in other words, of a vibrato and a tremolo.

Accordingly, it is the general object of the present invention to improve the quality of music produced by electronic devices. A particular object of the invention is to provide means for conferring upon the decay of electronically generated tones fluctuations in pitch or in amplitude or simultaneously in both to simulate the acoustic effect of a reverberantauditorium.

Further, it is an object of the invention to provide the operator of the instrument with means enabling him to control at will the pitch and am- Dlitude fluctuations above mentioned since it is enerally desirable to have less reverberation for fast music than for slow music and also more reverberation for detached chords, especially the last one.

A feature of the invention is the use of three relaxation oscillators, one of these serving, as in the devices of the prior art, to generate the periodicelectrical current which, through a loud speaker, produces a musical tone when a control key is operated. The two others act, either singly or together, when the operator by releasing a key initiates the decay of the sustained tone and serve to add to that tone the aforementioned fluctuations in pitch and amplitude.

Another feature of the invention is the provi- T 5 sion of means for automatically controlling the rate of onset of the tone when the control key i operated and similarly automatically controlling the rate of decay of the tone when the control key is released. I

The object stated, as well as other objects which will occur to those familiar/with this art, is accomplished by the apparatus of the invention which will be understood both in structure and operation from the following description illustrated by the accompanying drawing, in which:

Fig. l exhibits a preferred embodiment of the invention, omitting unessential details; and

Fig. 2 symbolically represents a musical tone,

- at first steady and then subsiding with superimgo posed variations in pitch and amplitude.

In Fig.1 potentiometer It is connected across battery Ill and a suitable fraction of the volta e across potentiometer II is selected by tap l2 thereon to supply power for the operaton of reg5 laxaton oscillator P, generally indicated as included within the dotted outline at the upper left of the diagram. The oscillating circuit of oscillator P is composed of condenser C and inductance L in series between tap l2 and ground and shunted by tube 1 which may suitably be a l-watt neon tube. Switching means, not shown, may of course be used to open or close the circuit of battery Ill. When this circuit is closed, as shown. relaxation oscillations are set up in the circuit C-L-I, the fundamental frequencies of these oscillations being determined by the values chosen for C and L. These oscillations, rich in harmonies, are made available to the subsequent circuit by ta lsof potentiometer l4 shunted across inductance L with the interposition of stoppin condenser l6.

Tap l3 isconnected by conductor IE to control grid 11 of vacuum tube l8, which is suitably an RCA 6U7-G. In tube Il,-cathode I9 is connected 1 to suppressor grid 20; anode 2| is supplied withvoltage from 300-volt battery 22 through resistor- 23 and screen grid 24 is polarized from a selected portion of battery 22. The customary current supply or heater 25 is omitted from the figure. So far the circuit is conventional.

Cathode i8 is capacitatively coupled to ground through condenser Cl, preferablyan electrolytic condenser 0! about 25 microfarad capacity. when key K. is in the position shown cathode l9 68 is also coupled to ground by way or resistor 21 3 (about 80,000 ohms resistance), condenser C2 (about 6 microfarads) and 55-volt battery 2!. Cathode l9 acquires under these circumstances a voltage of about 52 volts positive to grid I! so that tube I8 is biased to cut-oil. Condenser Cl acquires a corresponding charge.

When key K is depressed downward against the tension of spring S, breaking contact I and making contact 2, the connection of cathode I9 is transferred from conductor 26 to resistor 29 leading directly to ground. Resistor 29 is appropriately of about 200 ohms resistance so that the charge of condenser Cl is rapidly reduced. Tube l8 becomes conductive and the relaxation oscillations received by grid H are ampllfled and transmitted through stopping condenser 30 to loud-speaker 3|. It may be useful but is not a necessary part of the present invention to introduce a network 32 to modify in relative amplitude the various harmonics present in the output of relaxation oscillator P and to include this network with amplifier 33 in circuit between tube l8 and loud-speaker l I.

At the same time that contact 2 is made by depressing key K contact, 3 is made with the result that resistor 84 in series with 70-volt battery 35 is connected between conductor 26 and ground. Battery 35 is so poled that its voltage adds to that of battery 28 and breaks down tube II, at the same time charging condenser C2 to the 75 volts maintained by tube II across its terminals. For this purpose tube It is suitably a voltage regulator tube such as the VR'75-30. The combination of tube II, condenser C2 and resistor 21 constitutes a second relaxation oscillator T. Under the conditions described, condenser C2 being 01' about c-microiarad capacitance and resister 21 in series with resistor 34, each of these resistors having about 80,000 ohms resistance, the oscillations of oscillator T have a. frequency of about 3 cycles per second. This frequency may be changed by varying condenser C2 and means for giving the operator control of this variation will be obvious.

Thus when key K is depressed the conductance of tube I8 is established in about one one-hundredth second and as long as the key remains depressed a sustained tone is produced from loudspeaker an, rich in harmonics, modified in relative amplitude by network 32 if this network is used. Registor 29 may be made variable under the control of the operator to retard or accelerate the acquisition of conductance by tube is thereby controlling the rate of onset of the tone produced.

By the release oi key K contacts I and 3 are broken and contact I is reestablished. The conductance of tube I8 decays as condenser Cl is recharged through condenser 02 and resistor 21. With the values stated above for these elements this recharge requires about four seconds. The tone emitted by loud-speaker ll correspondingly decays at a rate which may be controlled by varying the resistance of resistor 21. This control may also, by obvious means, be made available to the operator whereby he is given control oi the subsidence as well as of onset of the musical tone produced by loud-speaker II.

It will be clear that the operation of breaking ontact 3 and restoring contact I permits relaxation oscillator T to add its generated oscillations to aiiect the rate at which condenser CI recharges whereby the decay of conductance of tube It! proceeds at an average rate determined chiefly I by resistor 21 but fluctuating about this average in accordance with. the super-added oscillations of oscillator '11. The acoustic effect is that of a natural logarithmic decay will only inadequately reproduce auditorium efl'ects.

For musical purposes the auditorium itself is properly to be considered a part of the musical instrument played therein and it has been pointed out earlier in this disclosure that the air in the auditorium has its own natural vibrations which are excited by impact. The exciting impact may be relatively abrupt, as when the tone is started.

or relatively slow, as when the tone is stopped. In the latter case-a distinct vibrato is added to the decaying tone. The effect is well recognized and r uires here no further explanation. How it is simulated by the apparatus of the present invention will now be described.

Contacts 4 and 5, initially closed when key K is in the position shown, connect relaxation oscillator V, indicated within the dotted line at lower left in the figure, across inductance L in tone generating oscillator P. Contact 4 connects ground to one terminal of tube III which is suit;- ably also a l-watt neon tube. The other terminal of tube III is connected through condenser C3 and conductor 36 to the end of inductance L remote from ground. The junction of tube III in condenser C3 is connected through resistor 31, conductor 38, contact 5 and tap 39 to a selected point on potentiometer 40 which shunts battery 4|, the negative side of which is grounded, Varying the position of tap 33, which may also be placed under the operators control, varies the frequency of oscillator V by varying the resistance included between ground and the junction of tube III and condenser C3.

Oscillations in the circuit of oscillator V are ineffective until contacts 4 and 5, broken when key K is depressed to initiate the tone, are restored by the release of the key. on this release oscillations produced by the breakdown of tube III are superimposed on those of oscillator P and since tube [8 is still conductive though decreasingly so, the subsiding sound omitted from loudspeaker 3| is affected with a pitch fluctuation cor responding to the oscillations of the circuit of oscillator V. A

The subsiding tone is then affected with a vibrato as well as with a tremolo and the audi torium eiiect in respect both to standing wave patterns and to natural frequency of the enclosed air is completely simulated. It is of course possible by easily made changes in the apparatus to omit either the vibrato or the tremolo, if desired. It will be obvious that the operator may be provided with means for controlling independently the total decay time, the rate and amplitude of the tremolo and the rate and amplitude 01 the vibrato.

It will be understood that the detailed description is of one only of the tone generatois required for a complete keyboard. Condensers I30 and 230 are shown to which other tone generators identical with the circuit described may be connected to the sound translating devices. When desired, any number of such circuits may be provided.

There has been described method for an apparatus and a the addition of pitch and amplitude of said onset, a second circuit means fluctuations to a decaying tone produced by the operation of an electronic tone generator, but obviously the invention is ciflc forms of oscillating circuits shown in Fig. 1, and equivalents for any or all of these are within the scope of the described invention.

I What is claimed is: I

1. In an electrical-musical instrument, in combination, means for generating a musical tone of desired amplitude and pitch, control means on erable directly to effect the onset of said tone and operable reversely to efiect a first circuit means associated with said control means when operated directly to control the rate associated with said control means when operated reversely to control the rate of said decay, and electrical means activated by said second circuit means tor superimposing variations in amplitude and in pitch on said tone during its decay.

2. In an electrical musical instrument, in combination, means for generating a musical tone of desired amplitude and pitch, control means operable directly to effect the onset oi. said tone and operable reversely to eflect the decay of said tone,

a first circuit means with said control means when operated of said onset, a second circuit means with said control means when operated reversely to control the rate of said decay, means activated by said second circuit means for superimposing variations in amplitude on said tone during its decay.

and electrical not limited to the spethe decay of said tone,

directly to control the. rate associated r 3, In an electrical musicalinstrument, in combination, means for generating a musical tone oi desired amplitude and plt h. control means operable directly to effect the onset of said tone v and operable reversely to elect the decay of said acoustic variations in the ,rate of onset of the cult associated erated reversely to tone, a first circuit control means when means associated with said operated directly to control the rate of said onset, a second circuit means associated with said control means when operated reversely to control the rate of said decay, and

. electrical means activated by said second circuit 4 ing variations in pitch on said tone during its decay.

means for superim 4. In an electrical musical instrument, in combination, means including a first relaxation'oscillator for generating a musical tone of desired amplitude and pitch, manual control means operable directly to efiect the onset of the toneand tone, 3. second electrical cirwith said control means when 09- control the rate of decay of the-tone, and means including a second and a third relaxation oscillator activated by said second circuit tor superimposing on the tone as it decays variations in pitch and in amplitude.

5. In an electrical musical instrument provided with means for generating .a musical tone having desired amplitude and pitch and decaying aiter a finite interval, means for simulating auditorium reverberation during the decay of the tone including, in combination, control means operable directly to eflect the onset of the tone and operable reversely to effect the decay thereof, electrical circuit means associated with said control means when" operated reversely to control the rate of decay including at least one relaxation oscillator ac tivated by said circuit means for superimposing um'r amass-me or the tone, and electrical means tone durins its decay. 4 

